1. Field of the Invention
This invention generally relates to audio speaker systems and more specifically to dust barriers for loudspeakers used in such speaker systems.
2. Description of Related Art
A continuing effort is being applied to the development of loudspeakers for producing speaker systems that produce high-quality sound and that operate with maximum efficiency. This effort, in part, has been directed to developing new loudspeaker constructions, many of which are susceptible to damage from dust, particularly dust attracted by a magnetic field.
My U.S. Pat. No. 4,595,801 and U.S. patent application Ser. No. 09/251,815 filed Feb. 17, 1999 disclose dual cone loudspeakers with a primary speaker cone similar in function to a conventional dynamic loudspeaker mounted on a frame with a magnet structure. A secondary speaker cone mounts to a sub-frame on the back of the magnet structure and connects to the primary speaker cone through a rigid coupling device so the primary and secondary speaker cones move in unison. Sound waves from the secondary speaker cone travel through an orifice or throat through a center pole piece of the magnet structure and through an open center of the primary speaker cone radiating in the same direction as sound waves from the primary speaker cone. Consequently for a given excursion of the primary speaker cone my dual cone structure generates a sound having a greater sound volume than the primary cone alone by virtue of the simultaneous excursions of both the primary and secondary speaker cones that move a greater air volume for a given speaker cone displacement.
This dual cone speaker is one example of a speaker in which a single speaker cone or front speaker cone has an annular shape and a central orifice or throat. Dust can be attracted to the permanent magnet through the central orifice. If such particles accumulate in the air gap between a voice coil and the magnet, they can impede voice coil and speaker motion. When this occurs, the speaker""s sound quality deteriorates. In more extreme situations, the accumulated attracted dust can cause permanent damage to the loudspeaker. What is needed is an apparatus or methodology for preventing the accumulation of attracted dust in the air gap, particularly in bass frequency loudspeakers in which a speaker cone undergoes a large linear displacement and requires high intensity magnetic fields in the air gap.
Therefore it is an object of this invention to provide a dust barrier that minimizes dust accumulated in the air gap of a loudspeaker.
Another object of this invention is to provide a loudspeaker in which magnetically attracted dust particles are blocked physically from entering the air gap between a voice coil and speaker magnet.
In accordance with this invention, a loudspeaker with a frame that carries an annular speaker cone having a central opening driven by a voice coil on a bobbin in a magnetic field produced across an annular air gap in a magnetic structure that includes a throat aligned with the loudspeaker cone central opening. A ring is affixed to the speaker cone at the periphery of the central opening and an annular seal overlies a portion of the magnet structure within the throat. The ring operatively connects to the voice bobbin and the annular seal proximate the attachment of the speaker cone whereby the annular seal constitutes a barrier between the air gap and the throat thereby to block any dust that could be attracted into the air gap.